The development of efficient, low noise, high density power converters is a continuing goal in the field of power electronics. A power converter is a power processing circuit that converts an input AC or DC voltage or current into a specified DC output voltage or current. Power converters are employed in many applications including telecommunications and computer systems wherein commercial AC voltages are converted to the DC voltages needed to operate the systems. Power converters, however, generally produce electromagnetic interference (EMI) noise.
In the United States, the Federal Communications Commission (FCC) has promulgated two different standards regarding the EMI that may be emitted by an electronic device. Consumer electronics must meet a stringent Class B emissions standard. Commercial products, on the other hand, are regulated under a less stringent Class A emissions standard. Telecommunications equipment is regulated as commercial products under FCC regulations. In the European market, for instance, telecommunications equipment must meet the stricter emissions standard for consumer products. Power converters, therefore, must be designed to meet not only domestic EMI regulatory requirements, but also various international regulations.
Switching mode power converters are typically packaged in a metal chassis to limit EMI emissions. EMI noise often escapes the power converter, however, by traveling through the output power conductor. An output EMI filter, placed on a printed wiring board (PWB), is typically used to filter the EMI noise on the output power conductor. For high power, high current power converters, however, the output interface is often composed of bus bars. Exhibiting lower conduction losses, the bus bars are thus integral to the design of high power and high density power converters. The bus bars, however, must typically attach to the PWB through long conduction paths. The output EMI filter mounted on the PWB is therefore less effective, since some EMI noise may couple directly to the output bus bars, thus bypassing the output EMI filter.
Accordingly, what is needed in the art is a system and method for filtering the EMI noise generated by the power converters, thereby allowing the power converters to meet not only domestic EMI regulatory requirements, but also various international regulations.